Check for parent/mod as well as parent.mod in findext. Debian/Ubuntu ship a system-wide hgrc that loads extensions using the syntax hgext/extension=, rather than hgext.extension=. Although the extensions work correctly, hg help <extension> doesn't understand this form without this patch.

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  <td class="node"><a href="?cs=#node|short#">#desc|strip|firstline|escape#</a></td>
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